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Income Taxes (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Jan. 31, 2018
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Income Tax Contingency [Line Items]        
Effective income tax rate (as a percent)   25.00% 30.00%  
Production tax credits   $ 23 $ 28  
Deferred income tax benefit associated with convertible investment tax credits   36 $ 128  
Tax Cuts and Jobs Act of 2017, income tax expense (benefit)   $ 125    
Production tax credit (PTC), roll off period   10 years    
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax (expense) benefit       $ (6,500)
FPL [Member]        
Income Tax Contingency [Line Items]        
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax (expense) benefit       (4,500)
NextEra Energy Resources [Member]        
Income Tax Contingency [Line Items]        
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax (expense) benefit       $ (2,000)
Accounting Standards Update 2018-02 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]        
Income Tax Contingency [Line Items]        
Cumulative effect on retained earnings, after tax $ (16)